Method of assembling electrodynamic sound reproducers



May 16, 1933. w. E. HOLLAND METHOD OF ASSEMBLING ELECTRODYNAMIC SOUND REPRODUCERS Filed Jan. 28, 1950 a aha @7 6 Patented May 16, 1933 UNITED STATES PAENT QFHQE WALTER E. HOLLAND, or

PHILADELPHIA, PENNSYLVANIA, Assre-non' T0 PHILADEL- PHIA STORAGE BATTERY COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A COR PORATION OF PENNSYLVANIA IMETHOD OF ASSEMBLINIG ELECTROIDYNAMIC SOUND REPROD'UQERS Application filed January 28, 1930. Serial No. 423,973.

This invention relates to improvements in methods of assembling electrodynamic sound reproducers.

Sound reproducers of this type employ a diaphragm having attached thereto a voice coil which operates within a restricted gap between pole pieces either permanently magnetized or having associated" therewith a second coil for setting up a magnetic field. In operation, the voice coil is energized by signals from the source, and movement of the coil in the magnetic field actuates the diaphragm and effects a reproductionof the signal. By reason of the restricted character of the space within which the voice coil operates and the limitations imposed by the mechanical structure, it has been a relatively difiicult operation to properly center the voice coil in the gap between the pole pieces, a condition which is essential to a proper operation of the reproducer.

The principal object of the present invention is to provide a simple and accurate method for centering the voice coil in the gap between the pole pieces within which it operates, as set forth above.

In the attached drawing:

Figure 1 is a diagrammatic sectional view illustrating enough of the assembly of an electrodynamic sound reproducer to afford a thorough understanding of the present invention, and

Fig. 2 is a wiring diagram further illustrating the invention.

With reference to Fig. 1 of the drawing, 1 is the diaphragm of an electrodynamic sound reproducer, and 2 is the diaphragnn actuating voice coil supported upon a hollow cylindrical foundation projecting from the apex portion of the diaphragm. 3 and 4: are pole pieces forming a restricted gap within which the coil 2 operates, and 5 is' a field coil, which surrounds the. pole piece 4 as illustrated. In accordance with the invention set forth in the copending United States application Serial Number 375,848, the coil 2 in the present instance is main- .tained in a properly adjusted position within the gap between the pole pieces by securing the diaphragm, through the medium the resultant be made to center itself within the gap'beof a screw 6 and a flexible integral web 7 at the apex end of the conical diaphragm,

to the end of the pole piece 4. y

.I have discovered that the operation of centering the coil 2 between the pole pieces may be materially facilitated and simplified by energizing the coils,spreferably under conditions approximating those [of actual service in signal reproduction. I have found, for example, that by energizing the 'fieldf60 coil 5 from a suitable source of potential, and by thcn subjecting the coil 2 to the effect of an oscillating current, preferably of a low frequency, the coil 2, if left free, will.

tween the pole pieces 3 and In assembling the reproducer, therefore, the screw 6 or other means for maintaining the coil.

rarily inoperative by removal or loosening V and the coils energized as specified, with the result that the coil 2 will center itself within the gap and may then be secured in this centered position by tightening the screw 6 while the coil is oscillating, or by render- 7 ing effective the equivalent means for retaining the coil in the proper adjusted position. In this instance, during the centering operation, the diaphragm is left free to, move about in accordance with the move-"' ment of the voice coil.

A simple and effective method forconducting the operation is to connect the reproducer, where intended for radio r'eception, in the circuit of a radio receiver and B5 to operate the latter at a relatively high volume, thereafter tightening the screw or rendering the anchoring means operative to; retain the coil in the centered position which, it will assume upon energization of the coils;

In the diagrammatic view of Fig. '2, the voice coil 2is shown connected in circuit with'an oscillator 8 producing, say, 60 cycle alternating current, while the coil 5 withiin. whose field the coil 2 is positioned is con- -nected to a source 9 of direct current, this quency for energizing the coil 2 during aidjustment, assurance is had that under normal operating conditions in actual service there will be no contact between the coil and the pole pieces with a resultant production of extraneous noise.

In another successfully employed method of assembly employing the principle, the diaphragm is secured in its supporting frame or housing with the coil 2 approximately centered etween the pole pieces but with the screw (3 unsecured. The diaphragm securing means consists in the present instance of screws 10 which passthrough and secure to the frame ll the flexible edge portion 12, which edge portion may be an integral part 01' the diaphragm or an annulus otsott leather orthe like secured to the diaphragm. After tightening the screws 10, the coils 2 and 5 are energized as set forth above, which. results in oscillation of the coil 2 between the pole pieces. lithe coil 2 is properly centered, it oscillates freely and Without contact with the pole pieces regardless of the volume of the oscillating energizing current, and the screw 6 may then be tightened to secure the coil in position. If the coil 2 does not oscillate freely, a proper adjustment of the coil in its gap may be obtained by exerting transverse pressure on the diaphragm and varying the point at which the pressure is applied until free oscillation oi' the coil within the gap is obtained, after which and while the said rectifying pressure is still effective the screw 6 is tightened to secure the coil in the adjusted position. i

I claim:

1. The method which consists in establishing a magnetic field through the medium of closelypositioned pole pieces, locating a coil within the gap between said pole pieces, effecting an axial oscillation of the coil by energizing the coil from a source of alternating current, and fixing the axis of said oscillation while the oscillation is in progress.

2. The method which consists in establishing a magnetic field through the medium of closely positioned pole pieces, locating a coil within the gap between said pole pieces energizing the coil from a source of alternating current to thereby etl'ect centering of the coil within the gap, and securing saidcoil in the centered position.

3. The method which consists in establishing a magnetic field through the medium of closely positioned pole pieces, locating a coil within the gap between said pole pieces, effecting an axial oscillation of the coil by energizing the coil from a source of alternating current thereby adjusting the coil within thegap to ailord freedom of oscillation Without contact with the pole pieces, and transversely fixing the coil in the ad- .justed position. 

